Method for parameter set reference in coded video stream

ABSTRACT

A method of decoding an encoded video bitstream using at least one processor, including obtaining a coded video sequence from the encoded video bitstream; obtaining a picture unit from the coded video sequence; obtaining a PH NAL unit included in the picture unit; obtaining at least one coded slice NAL unit included in the picture unit; decoding a coded picture based on the PH NAL unit, the at least one coded slice NAL unit a PPS NAL unit obtained from the coded video sequence, and am SPS NAL unit obtained from the coded video sequence; and outputting the decoded picture, wherein the SPS NAL unit is available to the at least one processor before the PPS NAL unit, and wherein the PPS NAL unit is available to the at least one processor before the PH NAL unit and the at least one coded slice NAL unit.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority from 35 U.S.C. § 119 to U.S.Provisional Application No. 62/954,099, filed on Dec. 27, 2019, in theUnited States Patent & Trademark Office, the disclosure of which isincorporated herein by reference in its entirety.

FIELD

The disclosed subject matter relates to video coding and decoding, andmore specifically, to parameter set reference and scope in a coded videostream in a coded video stream.

BACKGROUND

Video coding and decoding using inter-picture prediction with motioncompensation has been known. Uncompressed digital video can consist of aseries of pictures, each picture having a spatial dimension of, forexample, 1920×1080 luminance samples and associated chrominance samples.The series of pictures can have a fixed or variable picture rate(informally also known as frame rate), of, for example 60 pictures persecond or 60 Hz. Uncompressed video has significant bitraterequirements. For example, 1080p60 4:2:0 video at 8 bit per sample(1920×1080 luminance sample resolution at 60 Hz frame rate) requiresclose to 1.5 Gbit/s bandwidth. An hour of such video requires more than600 GByte of storage space.

One purpose of video coding and decoding can be the reduction ofredundancy in the input video signal, through compression. Compressioncan help reducing aforementioned bandwidth or storage spacerequirements, in some cases by two orders of magnitude or more. Bothlossless and lossy compression, as well as a combination thereof can beemployed. Lossless compression refers to techniques where an exact copyof the original signal can be reconstructed from the compressed originalsignal. When using lossy compression, the reconstructed signal may notbe identical to the original signal, but the distortion between originaland reconstructed signal is small enough to make the reconstructedsignal useful for the intended application. In the case of video, lossycompression is widely employed. The amount of distortion tolerateddepends on the application; for example, users of certain consumerstreaming applications may tolerate higher distortion than users oftelevision contribution applications. The compression ratio achievablecan reflect that: higher allowable/tolerable distortion can yield highercompression ratios.

A video encoder and decoder can utilize techniques from several broadcategories, including, for example, motion compensation, transform,quantization, and entropy coding, some of which will be introducedbelow.

Historically, video encoders and decoders tended to operate on a givenpicture size that was, in most cases, defined and stayed constant for acoded video sequence (CVS), Group of Pictures (GOP), or a similarmulti-picture timeframe. For example, in MPEG-2, system designs areknown to change the horizontal resolution (and, thereby, the picturesize) dependent on factors such as activity of the scene, but only at Ipictures, hence typically for a GOP. The resampling of referencepictures for use of different resolutions within a CVS is known, forexample, from ITU-T Rec. H.263 Annex P. However, here the picture sizedoes not change, only the reference pictures are being resampled,resulting potentially in only parts of the picture canvas being used (incase of downsampling), or only parts of the scene being captured (incase of upsampling). Further, H.263 Annex Q allows the resampling of anindividual macroblock by a factor of two (in each dimension), upward ordownward. Again, the picture size remains the same. The size of amacroblock is fixed in H.263, and therefore does not need to besignaled.

Changes of picture size in predicted pictures became more mainstream inmodern video coding. For example, VP9 allows reference pictureresampling and change of resolution for a whole picture. Similarly,certain proposals made towards VVC (including, for example, Hendry, et.al, “On adaptive resolution change (ARC) for VVC”, Joint Video Teamdocument WET-M0135-v1, Jan. 9-19, 2019, incorporated herein in itsentirety) allow for resampling of whole reference pictures todifferent—higher or lower—resolutions. In that document, differentcandidate resolutions are suggested to be coded in the sequenceparameter set and referred to by per-picture syntax elements in thepicture parameter set.

SUMMARY

In an embodiment, there is provided a method of decoding an encodedvideo bitstream using at least one processor, including obtaining acoded video sequence from the encoded video bitstream; obtaining apicture unit from the coded video sequence; obtaining a picture header(PH) network abstraction layer (NAL) unit included in the picture unit;obtaining at least one coded slice NAL unit included in the pictureunit; decoding a coded picture based on the PH NAL unit, the at leastone coded slice NAL unit, a picture parameter set (PPS) included in aPPS NAL unit obtained from the coded video sequence, and a sequenceparameter set (SPS) included in an SPS NAL unit obtained from the codedvideo sequence; and outputting the decoded picture, wherein the SPS NALunit is available to the at least one processor before the PPS NAL unit,and wherein the PPS NAL unit is available to the at least one processorbefore the PH NAL unit and the at least one coded slice NAL unit.

In an embodiment, there is provided a device for decoding an encodedvideo bitstream, including at least one memory configured to storeprogram code; and at least one processor configured to read the programcode and operate as instructed by the program code, the program codeincluding: first obtaining code configured to cause the at least oneprocessor to obtain a coded video sequence from the encoded videobitstream; second obtaining code configured to cause the at least oneprocessor to obtain a picture unit from the coded video sequence; thirdobtaining code configured to cause the at least one processor to obtaina picture header (PH) network abstraction layer (NAL) unit included inthe picture unit; fourth obtaining code configured to cause the at leastone processor to obtain at least one coded slice NAL unit included inthe picture unit; decoding code configured to cause the at least oneprocessor to a coded picture based on the PH NAL unit, the at least onecoded slice NAL unit, a picture parameter set (PPS) included in a PPSNAL unit obtained from the coded video sequence, and a sequenceparameter set (SPS) included in an SPS NAL unit obtained from the codedvideo sequence; and output code configured to cause the at least oneprocessor to output the decoded picture, wherein the SPS NAL unit isavailable to the at least one processor before the PPS NAL unit, andwherein the PPS NAL unit is available to the at least one processorbefore the PH NAL unit and the at least one coded slice NAL unit.

In an embodiment, there is provided a non-transitory computer-readablemedium storing instructions, the instructions including: one or moreinstructions that, when executed by one or more processors of a devicefor decoding an encoded video bitstream, cause the one or moreprocessors to: obtain a coded video sequence from the encoded videobitstream; obtain a picture unit from the coded video sequence; obtain apicture header (PH) network abstraction layer (NAL) unit included in thepicture unit; obtain at least one coded slice NAL unit included in thepicture unit; decode a coded picture based on the PH NAL unit, the atleast one coded slice NAL unit, a picture parameter set (PPS) includedin a PPS NAL unit obtained from the coded video sequence, and a sequenceparameter set (SPS) included in an SPS NAL unit obtained from the codedvideo sequence; and output the decoded picture, wherein the SPS NAL unitis available to one or more processors before the PPS NAL unit, andwherein the PPS NAL unit is available one or more processors before thePH NAL unit and the at least one coded slice NAL unit.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features, the nature, and various advantages of the disclosedsubject matter will be more apparent from the following detaileddescription and the accompanying drawings in which:

FIG. 1 is a schematic illustration of a simplified block diagram of acommunication system in accordance with an embodiment.

FIG. 2 is a schematic illustration of a simplified block diagram of acommunication system in accordance with an embodiment.

FIG. 3 is a schematic illustration of a simplified block diagram of adecoder in accordance with an embodiment.

FIG. 4 is a schematic illustration of a simplified block diagram of anencoder in accordance with an embodiment.

FIGS. 5A-5E are schematic illustrations of options for signaling ARCparameters in accordance with an embodiment, in accordance with anembodiment.

FIGS. 6A-6B are schematic illustration of examples of syntax tables inaccordance with an embodiment.

FIG. 7 is an example of prediction structure for scalability withadaptive resolution change, in accordance with an embodiment.

FIG. 8 is an example of a syntax table in accordance with an embodiment.

FIG. 9 is a schematic illustration of a simplified block diagram ofparsing and decoding POC cycle per access unit and access unit countvalue, in accordance with an embodiment.

FIG. 10 is a schematic illustration of a video bitstream structureincluding multi-layered sub-pictures, in accordance with an embodiment.

FIG. 11 is a schematic illustration of a display of the selectedsub-picture with an enhanced resolution, in accordance with anembodiment.

FIG. 12 is a block diagram of a decoding and display process for a videobitstream including multi-layered sub-pictures, in accordance with anembodiment.

FIG. 13 is a schematic illustration of 360 video display with anenhancement layer of a sub-picture, in accordance with an embodiment.

FIG. 14 is an example of a layout information of sub-pictures and itscorresponding layer and picture prediction structure, in accordance withan embodiment.

FIG. 15 is an example of a layout information of sub-pictures and itscorresponding layer and picture prediction structure, with spatialscalability modality of local region, in accordance with an embodiment.

FIGS. 16A-16B are examples of syntax tables for sub-picture layoutinformation, in accordance with embodiments.

FIG. 17 is an example of a syntax table of SEI message for sub-picturelayout information, in accordance with an embodiment.

FIG. 18 is an example of a syntax table to indicate output layers andprofile/tier/level information for each output layer set, in accordancewith an embodiment.

FIG. 19 is an example of a syntax table to indicate output layer mode onfor each output layer set, in accordance with an embodiment.

FIG. 20 is an example of a syntax table to indicate the presentsubpicture of each layer for each output layer set, in accordance withan embodiment.

FIG. 21 is a flowchart of an example process for decoding an encodedvideo bitstream in accordance with an embodiment.

FIG. 22 is a schematic illustration of a computer system in accordancewith an embodiment.

DETAILED DESCRIPTION

FIG. 1 illustrates a simplified block diagram of a communication system(100) according to an embodiment of the present disclosure. The system(100) may include at least two terminals (110-120) interconnected via anetwork (150). For unidirectional transmission of data, a first terminal(110) may code video data at a local location for transmission to theother terminal (120) via the network (150). The second terminal (120)may receive the coded video data of the other terminal from the network(150), decode the coded data and display the recovered video data.Unidirectional data transmission may be common in media servingapplications and the like.

FIG. 1 illustrates a second pair of terminals (130, 140) provided tosupport bidirectional transmission of coded video that may occur, forexample, during videoconferencing. For bidirectional transmission ofdata, each terminal (130, 140) may code video data captured at a locallocation for transmission to the other terminal via the network (150).Each terminal (130, 140) also may receive the coded video datatransmitted by the other terminal, may decode the coded data and maydisplay the recovered video data at a local display device.

In FIG. 1 , the terminals (110-140) may be illustrated as servers,personal computers and smart phones but the principles of the presentdisclosure may be not so limited. Embodiments of the present disclosurefind application with laptop computers, tablet computers, media playersand/or dedicated video conferencing equipment. The network (150)represents any number of networks that convey coded video data among theterminals (110-140), including for example wireline and/or wirelesscommunication networks. The communication network (150) may exchangedata in circuit-switched and/or packet-switched channels. Representativenetworks include telecommunications networks, local area networks, widearea networks and/or the Internet. For the purposes of the presentdiscussion, the architecture and topology of the network (150) may beimmaterial to the operation of the present disclosure unless explainedherein below.

FIG. 2 illustrates, as an example for an application for the disclosedsubject matter, the placement of a video encoder and decoder in astreaming environment. The disclosed subject matter can be equallyapplicable to other video enabled applications, including, for example,video conferencing, digital TV, storing of compressed video on digitalmedia including CD, DVD, memory stick and the like, and so on.

A streaming system may include a capture subsystem (213), that caninclude a video source (201), for example a digital camera, creating afor example uncompressed video sample stream (202). That sample stream(202), depicted as a bold line to emphasize a high data volume whencompared to encoded video bitstreams, can be processed by an encoder(203) coupled to the camera (201). The encoder (203) can includehardware, software, or a combination thereof to enable or implementaspects of the disclosed subject matter as described in more detailbelow. The encoded video bitstream (204), depicted as a thin line toemphasize the lower data volume when compared to the sample stream, canbe stored on a streaming server (205) for future use. One or morestreaming clients (206, 208) can access the streaming server (205) toretrieve copies (207, 209) of the encoded video bitstream (204). Aclient (206) can include a video decoder (210) which decodes theincoming copy of the encoded video bitstream (207) and creates anoutgoing video sample stream (211) that can be rendered on a display(212) or other rendering device (not depicted). In some streamingsystems, the video bitstreams (204, 207, 209) can be encoded accordingto certain video coding/compression standards. Examples of thosestandards include ITU-T Recommendation H.265. Under development is avideo coding standard informally known as Versatile Video Coding or VVC.The disclosed subject matter may be used in the context of VVC.

FIG. 3 may be a functional block diagram of a video decoder (210)according to an embodiment of the present disclosure.

A receiver (310) may receive one or more codec video sequences to bedecoded by the decoder (210); in the same or another embodiment, onecoded video sequence at a time, where the decoding of each coded videosequence is independent from other coded video sequences. The codedvideo sequence may be received from a channel (312), which may be ahardware/software link to a storage device which stores the encodedvideo data. The receiver (310) may receive the encoded video data withother data, for example, coded audio data and/or ancillary data streams,that may be forwarded to their respective using entities (not depicted).The receiver (310) may separate the coded video sequence from the otherdata. To combat network jitter, a buffer memory (315) may be coupled inbetween receiver (310) and entropy decoder/parser (320) (“parser”henceforth). When receiver (310) is receiving data from a store/forwarddevice of sufficient bandwidth and controllability, or from anisosychronous network, the buffer (315) may not be needed, or can besmall. For use on best effort packet networks such as the Internet, thebuffer (315) may be required, can be comparatively large and canadvantageously of adaptive size.

The video decoder (210) may include a parser (320) to reconstructsymbols (321) from the entropy coded video sequence. Categories of thosesymbols include information used to manage operation of the decoder(210), and potentially information to control a rendering device such asa display (212) that is not an integral part of the decoder but can becoupled to it, as was shown in FIG. 3 . The control information for therendering device(s) may be in the form of Supplementary EnhancementInformation (SEI messages) or Video Usability Information (VUI)parameter set fragments (not depicted). The parser (320) mayparse/entropy-decode the coded video sequence received. The coding ofthe coded video sequence can be in accordance with a video codingtechnology or standard, and can follow principles well known to a personskilled in the art, including variable length coding, Huffman coding,arithmetic coding with or without context sensitivity, and so forth. Theparser (320) may extract from the coded video sequence, a set ofsubgroup parameters for at least one of the subgroups of pixels in thevideo decoder, based upon at least one parameter corresponding to thegroup. Subgroups can include Groups of Pictures (GOPs), pictures,sub-pictures, tiles, slices, bricks, macroblocks, Coding Tree Units(CTUs) Coding Units (CUs), blocks, Transform Units (TUs), PredictionUnits (PUs) and so forth. A tile may indicate a rectangular region ofCU/CTUs within a particular tile column and row in a picture. A brickmay indicate a rectangular region of CU/CTU rows within a particulartile. A slice may indicate one or more bricks of a picture, which arecontained in an NAL unit. A sub-picture may indicate an rectangularregion of one or more slices in a picture. The entropy decoder/parsermay also extract from the coded video sequence information such astransform coefficients, quantizer parameter values, motion vectors, andso forth.

The parser (320) may perform entropy decoding/parsing operation on thevideo sequence received from the buffer (315), so to create symbols(321).

Reconstruction of the symbols (321) can involve multiple different unitsdepending on the type of the coded video picture or parts thereof (suchas: inter and intra picture, inter and intra block), and other factors.Which units are involved, and how, can be controlled by the subgroupcontrol information that was parsed from the coded video sequence by theparser (320). The flow of such subgroup control information between theparser (320) and the multiple units below is not depicted for clarity.

Beyond the functional blocks already mentioned, decoder 210 can beconceptually subdivided into a number of functional units as describedbelow. In a practical implementation operating under commercialconstraints, many of these units interact closely with each other andcan, at least partly, be integrated into each other. However, for thepurpose of describing the disclosed subject matter, the conceptualsubdivision into the functional units below is appropriate.

A first unit is the scaler/inverse transform unit (351). Thescaler/inverse transform unit (351) receives quantized transformcoefficient as well as control information, including which transform touse, block size, quantization factor, quantization scaling matrices,etc. as symbol(s) (321) from the parser (320). It can output blockscomprising sample values, that can be input into aggregator (355).

In some cases, the output samples of the scaler/inverse transform (351)can pertain to an intra coded block; that is: a block that is not usingpredictive information from previously reconstructed pictures, but canuse predictive information from previously reconstructed parts of thecurrent picture. Such predictive information can be provided by an intrapicture prediction unit (352). In some cases, the intra pictureprediction unit (352) generates a block of the same size and shape ofthe block under reconstruction, using surrounding already reconstructedinformation fetched from the current (partly reconstructed) picture(358). The aggregator (355), in some cases, adds, on a per sample basis,the prediction information the intra prediction unit (352) has generatedto the output sample information as provided by the scaler/inversetransform unit (351).

In other cases, the output samples of the scaler/inverse transform unit(351) can pertain to an inter coded, and potentially motion compensatedblock. In such a case, a Motion Compensation Prediction unit (353) canaccess reference picture memory (357) to fetch samples used forprediction. After motion compensating the fetched samples in accordancewith the symbols (321) pertaining to the block, these samples can beadded by the aggregator (355) to the output of the scaler/inversetransform unit (in this case called the residual samples or residualsignal) so to generate output sample information. The addresses withinthe reference picture memory form where the motion compensation unitfetches prediction samples can be controlled by motion vectors,available to the motion compensation unit in the form of symbols (321)that can have, for example X, Y, and reference picture components.Motion compensation also can include interpolation of sample values asfetched from the reference picture memory when sub-sample exact motionvectors are in use, motion vector prediction mechanisms, and so forth.

The output samples of the aggregator (355) can be subject to variousloop filtering techniques in the loop filter unit (356). Videocompression technologies can include in-loop filter technologies thatare controlled by parameters included in the coded video bitstream andmade available to the loop filter unit (356) as symbols (321) from theparser (320), but can also be responsive to meta-information obtainedduring the decoding of previous (in decoding order) parts of the codedpicture or coded video sequence, as well as responsive to previouslyreconstructed and loop-filtered sample values.

The output of the loop filter unit (356) can be a sample stream that canbe output to the render device (212) as well as stored in the referencepicture memory for use in future inter-picture prediction.

Certain coded pictures, once fully reconstructed, can be used asreference pictures for future prediction. Once a coded picture is fullyreconstructed and the coded picture has been identified as a referencepicture (by, for example, parser (320)), the current reference picture(358) can become part of the reference picture buffer (357), and a freshcurrent picture memory can be reallocated before commencing thereconstruction of the following coded picture.

The video decoder 210 may perform decoding operations according to apredetermined video compression technology that may be documented in astandard, such as ITU-T Rec. H.265. The coded video sequence may conformto a syntax specified by the video compression technology or standardbeing used, in the sense that it adheres to the syntax of the videocompression technology or standard, as specified in the videocompression technology document or standard and specifically in theprofiles document therein. Also necessary for compliance can be that thecomplexity of the coded video sequence is within bounds as defined bythe level of the video compression technology or standard. In somecases, levels restrict the maximum picture size, maximum frame rate,maximum reconstruction sample rate (measured in, for example megasamplesper second), maximum reference picture size, and so on. Limits set bylevels can, in some cases, be further restricted through HypotheticalReference Decoder (HRD) specifications and metadata for HRD buffermanagement signaled in the coded video sequence.

In an embodiment, the receiver (310) may receive additional (redundant)data with the encoded video. The additional data may be included as partof the coded video sequence(s). The additional data may be used by thevideo decoder (210) to properly decode the data and/or to moreaccurately reconstruct the original video data. Additional data can bein the form of, for example, temporal, spatial, or SNR enhancementlayers, redundant slices, redundant pictures, forward error correctioncodes, and so on.

FIG. 4 may be a functional block diagram of a video encoder (203)according to an embodiment of the present disclosure.

The encoder (203) may receive video samples from a video source (201)(that is not part of the encoder) that may capture video image(s) to becoded by the encoder (203).

The video source (201) may provide the source video sequence to be codedby the encoder (203) in the form of a digital video sample stream thatcan be of any suitable bit depth (for example: 8 bit, 10 bit, 12 bit, .. . ), any colorspace (for example, BT.601 Y CrCB, RGB, . . . ) and anysuitable sampling structure (for example Y CrCb 4:2:0, Y CrCb 4:4:4). Ina media serving system, the video source (201) may be a storage devicestoring previously prepared video. In a videoconferencing system, thevideo source (203) may be a camera that captures local image informationas a video sequence. Video data may be provided as a plurality ofindividual pictures that impart motion when viewed in sequence. Thepictures themselves may be organized as a spatial array of pixels,wherein each pixel can comprise one or more sample depending on thesampling structure, color space, etc. in use. A person skilled in theart can readily understand the relationship between pixels and samples.The description below focusses on samples.

According to an embodiment, the encoder (203) may code and compress thepictures of the source video sequence into a coded video sequence (443)in real time or under any other time constraints as required by theapplication. Enforcing appropriate coding speed is one function ofController (450). Controller controls other functional units asdescribed below and is functionally coupled to these units. The couplingis not depicted for clarity. Parameters set by controller can includerate control related parameters (picture skip, quantizer, lambda valueof rate-distortion optimization techniques, . . . ), picture size, groupof pictures (GOP) layout, maximum motion vector search range, and soforth. A person skilled in the art can readily identify other functionsof controller (450) as they may pertain to video encoder (203) optimizedfor a certain system design.

Some video encoders operate in what a person skilled in the are readilyrecognizes as a “coding loop”. As an oversimplified description, acoding loop can consist of the encoding part of an encoder (430)(“source coder” henceforth) (responsible for creating symbols based onan input picture to be coded, and a reference picture(s)), and a (local)decoder (433) embedded in the encoder (203) that reconstructs thesymbols to create the sample data a (remote) decoder also would create(as any compression between symbols and coded video bitstream islossless in the video compression technologies considered in thedisclosed subject matter). That reconstructed sample stream is input tothe reference picture memory (434). As the decoding of a symbol streamleads to bit-exact results independent of decoder location (local orremote), the reference picture buffer content is also bit exact betweenlocal encoder and remote encoder. In other words, the prediction part ofan encoder “sees” as reference picture samples exactly the same samplevalues as a decoder would “see” when using prediction during decoding.This fundamental principle of reference picture synchronicity (andresulting drift, if synchronicity cannot be maintained, for examplebecause of channel errors) is well known to a person skilled in the art.

The operation of the “local” decoder (433) can be the same as of a“remote” decoder (210), which has already been described in detail abovein conjunction with FIG. 3 . Briefly referring also to FIG. 4 , however,as symbols are available and en/decoding of symbols to a coded videosequence by entropy coder (445) and parser (320) can be lossless, theentropy decoding parts of decoder (210), including channel (312),receiver (310), buffer (315), and parser (320) may not be fullyimplemented in local decoder (433).

An observation that can be made at this point is that any decodertechnology except the parsing/entropy decoding that is present in adecoder also necessarily needs to be present, in substantially identicalfunctional form, in a corresponding encoder. For this reason, thedisclosed subject matter focusses on decoder operation. The descriptionof encoder technologies can be abbreviated as they are the inverse ofthe comprehensively described decoder technologies. Only in certainareas a more detail description is required and provided below.

As part of its operation, the source coder (430) may perform motioncompensated predictive coding, which codes an input frame predictivelywith reference to one or more previously-coded frames from the videosequence that were designated as “reference frames.” In this manner, thecoding engine (432) codes differences between pixel blocks of an inputframe and pixel blocks of reference frame(s) that may be selected asprediction reference(s) to the input frame.

The local video decoder (433) may decode coded video data of frames thatmay be designated as reference frames, based on symbols created by thesource coder (430). Operations of the coding engine (432) mayadvantageously be lossy processes. When the coded video data may bedecoded at a video decoder (not shown in FIG. 4 ), the reconstructedvideo sequence typically may be a replica of the source video sequencewith some errors. The local video decoder (433) replicates decodingprocesses that may be performed by the video decoder on reference framesand may cause reconstructed reference frames to be stored in thereference picture cache (434). In this manner, the encoder (203) maystore copies of reconstructed reference frames locally that have commoncontent as the reconstructed reference frames that will be obtained by afar-end video decoder (absent transmission errors).

The predictor (435) may perform prediction searches for the codingengine (432). That is, for a new frame to be coded, the predictor (435)may search the reference picture memory (434) for sample data (ascandidate reference pixel blocks) or certain metadata such as referencepicture motion vectors, block shapes, and so on, that may serve as anappropriate prediction reference for the new pictures. The predictor(435) may operate on a sample block-by-pixel block basis to findappropriate prediction references. In some cases, as determined bysearch results obtained by the predictor (435), an input picture mayhave prediction references drawn from multiple reference pictures storedin the reference picture memory (434).

The controller (450) may manage coding operations of the video coder(430), including, for example, setting of parameters and subgroupparameters used for encoding the video data.

Output of all aforementioned functional units may be subjected toentropy coding in the entropy coder (445). The entropy coder translatesthe symbols as generated by the various functional units into a codedvideo sequence, by loss-less compressing the symbols according totechnologies known to a person skilled in the art as, for exampleHuffman coding, variable length coding, arithmetic coding, and so forth.

The transmitter (440) may buffer the coded video sequence(s) as createdby the entropy coder (445) to prepare it for transmission via acommunication channel (460), which may be a hardware/software link to astorage device which would store the encoded video data. The transmitter(440) may merge coded video data from the video coder (430) with otherdata to be transmitted, for example, coded audio data and/or ancillarydata streams (sources not shown).

The controller (450) may manage operation of the encoder (203). Duringcoding, the controller (450) may assign to each coded picture a certaincoded picture type, which may affect the coding techniques that may beapplied to the respective picture. For example, pictures often may beassigned as one of the following frame types:

An Intra Picture (I picture) may be one that may be coded and decodedwithout using any other frame in the sequence as a source of prediction.Some video codecs allow for different types of Intra pictures,including, for example Independent Decoder Refresh Pictures. A personskilled in the art is aware of those variants of I pictures and theirrespective applications and features.

A Predictive picture (P picture) may be one that may be coded anddecoded using intra prediction or inter prediction using at most onemotion vector and reference index to predict the sample values of eachblock.

A Bi-directionally Predictive Picture (B Picture) may be one that may becoded and decoded using intra prediction or inter prediction using atmost two motion vectors and reference indices to predict the samplevalues of each block. Similarly, multiple-predictive pictures can usemore than two reference pictures and associated metadata for thereconstruction of a single block.

Source pictures commonly may be subdivided spatially into a plurality ofsample blocks (for example, blocks of 4×4, 8×8, 4×8, or 16×16 sampleseach) and coded on a block-by-block basis. Blocks may be codedpredictively with reference to other (already coded) blocks asdetermined by the coding assignment applied to the blocks' respectivepictures. For example, blocks of I pictures may be codednon-predictively or they may be coded predictively with reference toalready coded blocks of the same picture (spatial prediction or intraprediction). Pixel blocks of P pictures may be coded non-predictively,via spatial prediction or via temporal prediction with reference to onepreviously coded reference pictures. Blocks of B pictures may be codednon-predictively, via spatial prediction or via temporal prediction withreference to one or two previously coded reference pictures.

The video coder (203) may perform coding operations according to apredetermined video coding technology or standard, such as ITU-T Rec.H.265. In its operation, the video coder (203) may perform variouscompression operations, including predictive coding operations thatexploit temporal and spatial redundancies in the input video sequence.The coded video data, therefore, may conform to a syntax specified bythe video coding technology or standard being used.

In an embodiment, the transmitter (440) may transmit additional datawith the encoded video. The video coder (430) may include such data aspart of the coded video sequence. Additional data may comprisetemporal/spatial/SNR enhancement layers, other forms of redundant datasuch as redundant pictures and slices, Supplementary EnhancementInformation (SEI) messages, Visual Usability Information (VUI) parameterset fragments, and so on.

Recently, compressed domain aggregation or extraction of multiplesemantically independent picture parts into a single video picture hasgained some attention. In particular, in the context of, for example,360 coding or certain surveillance applications, multiple semanticallyindependent source pictures (for examples the six cube surface of acube-projected 360 scene, or individual camera inputs in case of amulti-camera surveillance setup) may require separate adaptiveresolution settings to cope with different per-scene activity at a givenpoint in time. In other words, encoders, at a given point in time, maychoose to use different resampling factors for different semanticallyindependent pictures that make up the whole 360 or surveillance scene.When combined into a single picture, that, in turn, requires thatreference picture resampling is performed, and adaptive resolutioncoding signaling is available, for parts of a coded picture.

Below, a few terms will be introduced that will be referred to in theremainder of this description.

Sub-Picture may refer to a, in some cases, rectangular arrangement ofsamples, blocks, macroblocks, coding units, or similar entities that aresemantically grouped, and that may be independently coded in changedresolution. One or more sub-pictures may form a picture. One or morecoded sub-pictures may form a coded picture. One or more sub-picturesmay be assembled into a picture, and one or more sub pictures may beextracted from a picture. In certain environments, one or more codedsub-pictures may be assembled in the compressed domain withouttranscoding to the sample level into a coded picture, and in the same orother cases, one or more coded sub-pictures may be extracted from acoded picture in the compressed domain.

Adaptive Resolution Change (ARC) may refer to mechanisms that allow thechange of resolution of a picture or sub-picture within a coded videosequence, by the means of, for example, reference picture resampling.ARC parameters henceforth refer to the control information required toperform adaptive resolution change, that may include, for example,filter parameters, scaling factors, resolutions of output and/orreference pictures, various control flags, and so forth.

In embodiments coding and decoding may be performed on a single,semantically independent coded video picture. Before describing theimplication of coding/decoding of multiple sub pictures with independentARC parameters and its implied additional complexity, options forsignaling ARC parameters shall be described.

Referring to FIGS. 5A-5E, shown are several embodiments for signalingARC parameters. As noted with each of the embodiments, they may havecertain advantages and certain disadvantages from a coding efficiency,complexity, and architecture viewpoint. A video coding standard ortechnology may choose one or more of these embodiments, or options knownfrom related art, for signaling ARC parameters. The embodiments may notbe mutually exclusive, and conceivably may be interchanged based onapplication needs, standards technology involved, or encoder's choice.

Classes of ARC parameters may include:

-   -   up/downsample factors, separate or combined in X and Y dimension    -   up/downsample factors, with an addition of a temporal dimension,        indicating constant speed zoom in/out for a given number of        pictures    -   Either of the above two may involve the coding of one or more        presumably short syntax elements that may point into a table        containing the factor(s).    -   resolution, in X or Y dimension, in units of samples, blocks,        macroblocks, coding units (CUs), or any other suitable        granularity, of the input picture, output picture, reference        picture, coded picture, combined or separately. If there is more        than one resolution (such as, for example, one for input        picture, one for reference picture) then, in certain cases, one        set of values may be inferred to from another set of values.        Such could be gated, for example, by the use of flags. For a        more detailed example, see below.    -   “warping” coordinates akin those used in H.263 Annex P, again in        a suitable granularity as described above. H.263 Annex P defines        one efficient way to code such warping coordinates, but other,        potentially more efficient ways could conceivably also be        devised. For example, the variable length reversible,        “Huffman”-style coding of warping coordinates of Annex P could        be replaced by a suitable length binary coding, where the length        of the binary code word could, for example, be derived from a        maximum picture size, possibly multiplied by a certain factor        and offset by a certain value, so to allow for “warping” outside        of the maximum picture size's boundaries.    -   up or downsample filter parameters. In embodiments, there may be        only a single filter for up and/or downsampling. However, in        embodiments, it can be desirable to allow more flexibility in        filter design, and that may require to signaling of filter        parameters. Such parameters may be selected through an index in        a list of possible filter designs, the filter may be fully        specified (for example through a list of filter coefficients,        using suitable entropy coding techniques), the filter may be        implicitly selected through up/downsample ratios according which        in turn are signaled according to any of the mechanisms        mentioned above, and so forth.

Henceforth, the description assumes the coding of a finite set ofup/downsample factors (the same factor to be used in both X and Ydimension), indicated through a codeword. That codeword may be variablelength coded, for example using the Ext-Golomb code common for certainsyntax elements in video coding specifications such as H.264 and H.265.One suitable mapping of values to up/downsample factors can, forexample, be according to Table 1:

TABLE 1 Codeword Ext-Golomb Code Original/Target resolution 0 1 1/1 1010 1/1.5 (upscale by 50%) 2 011 1.5/1 (downscale by 50%) 3 00100 1/2(upscale by 100%) 4 00101 2/1 (downscale by 100%)

Many similar mappings could be devised according to the needs of anapplication and the capabilities of the up and downscale mechanismsavailable in a video compression technology or standard. The table couldbe extended to more values. Values may also be represented by entropycoding mechanisms other than Ext-Golomb codes, for example using binarycoding. That may have certain advantages when the resampling factorswere of interest outside the video processing engines (encoder anddecoder foremost) themselves, for example by MANEs. It should be notedthat, for situations where no resolution change is required, anExt-Golomb code can be chosen that is short; in the table above, only asingle bit. That can have a coding efficiency advantage over usingbinary codes for the most common case.

The number of entries in the table, as well as their semantics, may befully or partially configurable. For example, the basic outline of thetable may be conveyed in a “high” parameter set such as a sequence ordecoder parameter set. In embodiments, one or more such tables may bedefined in a video coding technology or standard, and may be selectedthrough for example a decoder or sequence parameter set.

Below is described how an upsample/downsample factor (ARC information),coded as described above, may be included in a video coding technologyor standard syntax. Similar considerations may apply to one, or a few,codewords controlling up/downsample filters. See below for a discussionwhen comparatively large amounts of data are required for a filter orother data structures.

As shown in FIG. 5A, H.263 Annex P includes the ARC information (502) inthe form of four warping coordinates into the picture header (501),specifically in the H.263 PLUSPTYPE (503) header extension. This can bea sensible design choice when a) there is a picture header available,and b) frequent changes of the ARC information are expected. However,the overhead when using H.263-style signaling can be quite high, andscaling factors may not pertain among picture boundaries as pictureheader can be of transient nature.

As shown in FIG. 5B, JVCET-M135-v1 includes the ARC referenceinformation (505) (an index) located in a picture parameter set (504),indexing a table (506) including target resolutions that in turn islocated inside a sequence parameter set (507). The placement of thepossible resolution in a table (506) in the sequence parameter set (507)can, according to verbal statements made by the authors, be justified byusing the SPS as an interoperability negotiation point during capabilityexchange. Resolution can change, within the limits set by the values inthe table (506) from picture to picture by referencing the appropriatepicture parameter set (504).

Referring to FIGS. 5C-5E, the following embodiments may exist to conveyARC information in a video bitstream. Each of those options has certainadvantages over embodiments described above. Embodiments may besimultaneously present in the same video coding technology or standard.

In embodiments, for example the embodiment shown in FIG. 5C, ARCinformation (509) such as a resampling (zoom) factor may be present in aslice header, GOP header, tile header, or tile group header. FIG. 5Cillustrates an embodiment in which tile group header (508) is used. Thiscan be adequate if the ARC information is small, such as a singlevariable length ue(v) or fixed length codeword of a few bits, forexample as shown above. Having the ARC information in a tile groupheader directly has the additional advantage of the ARC information maybe applicable to a sub picture represented by, for example, that tilegroup, rather than the whole picture. See also below. In addition, evenif the video compression technology or standard envisions only wholepicture adaptive resolution changes (in contrast to, for example, tilegroup based adaptive resolution changes), putting the ARC informationinto the tile group header vis a vis putting it into an H.263-stylepicture header has certain advantages from an error resilienceviewpoint.

In embodiments, for example the embodiment shown in FIG. 5D, the ARCinformation (512) itself may be present in an appropriate parameter setsuch as, for example, a picture parameter set, header parameter set,tile parameter set, adaptation parameter set, and so forth. FIG. 5Dillustrates an embodiment in which adaptation parameter set (511) isused. The scope of that parameter set can advantageously be no largerthan a picture, for example a tile group. The use of the ARC informationis implicit through the activation of the relevant parameter set. Forexample, when a video coding technology or standard contemplates onlypicture-based ARC, then a picture parameter set or equivalent may beappropriate.

In embodiments, for example the embodiment shown in FIG. 5E, ARCreference information (513) may be present in a Tile Group header (514)or a similar data structure. That reference information (513) can referto a subset of ARC information (515) available in a parameter set (516)with a scope beyond a single picture, for example a sequence parameterset, or decoder parameter set.

The additional level of indirection implied activation of a PPS from atile group header, PPS, SPS, as used in JVET-M0135-v1 appears to beunnecessary, as picture parameter sets, just as sequence parameter sets,can (and have in certain standards such as RFC3984) be used forcapability negotiation or announcements. If, however, the ARCinformation should be applicable to a sub picture represented, forexample, by a tile groups also, a parameter set with an activation scopelimited to a tile group, such as the Adaptation Parameter set or aHeader Parameter Set may be the better choice. Also, if the ARCinformation is of more than negligible size—for example contains filtercontrol information such as numerous filter coefficients—then aparameter may be a better choice than using a header (508) directly froma coding efficiency viewpoint, as those settings may be reusable byfuture pictures or sub-pictures by referencing the same parameter set.

When using the sequence parameter set or another higher parameter setwith a scope spanning multiple pictures, certain considerations mayapply:

-   -   1. The parameter set to store the ARC information table (516)        can, in some cases, be the sequence parameter set, but in other        cases advantageously the decoder parameter set. The decoder        parameter set can have an activation scope of multiple CVSs,        namely the coded video stream, i.e. all coded video bits from        session start until session teardown. Such a scope may be more        appropriate because possible ARC factors may be a decoder        feature, possibly implemented in hardware, and hardware features        tend not to change with any CVS (which in at least some        entertainment systems is a Group of Pictures, one second or less        in length). That said, putting the table into the sequence        parameter set is expressly included in the placement options        described herein, in particular in conjunction with point 2        below.    -   2. The ARC reference information (513) may advantageously be        placed directly into the picture/slice tile/GOP/tile group        header, for example tile group header (514) rather than into the        picture parameter set as in JVCET-M0135-v1. For example, when an        encoder wants to change a single value in a picture parameter        set, such as for example the ARC reference information, then it        has to create a new PPS and reference that new PPS. Assume that        only the ARC reference information changes, but other        information such as, for example, the quantization matrix        information in the PPS stays. Such information can be of        substantial size, and would need to be retransmitted to make the        new PPS complete. As the ARC reference information (513) may be        a single codeword, such as the index into the table and that        would be the only value that changes, it would be cumbersome and        wasteful to retransmit all the, for example, quantization matrix        information. Insofar, can be considerably better from a coding        efficiency viewpoint to avoid the indirection through the PPS,        as proposed in JVET-M0135-v1. Similarly, putting the ARC        reference information into the PPS has the additional        disadvantage that the ARC information referenced by the ARC        reference information (513) may apply to the whole picture and        not to a sub-picture, as the scope of a picture parameter set        activation is a picture.

In the same or another embodiment, the signaling of ARC parameters canfollow a detailed example as outlined in FIGS. 6A-6B. FIGS. 6A-6B depictsyntax diagrams in a type of representation using a notation whichroughly follows C-style programming, as for example used in video codingstandards since at least 1993. Lines in boldface indicate syntaxelements present in the bitstream, lines without boldface often indicatecontrol flow or the setting of variables.

As shown in FIG. 6A, a tile group header (601) as an exemplary syntaxstructure of a header applicable to a (possibly rectangular) part of apicture can conditionally contain, a variable length, Exp-Golomb codedsyntax element dec_pic_size_idx (602) (depicted in boldface). Thepresence of this syntax element in the tile group header can be gated onthe use of adaptive resolution (603)—here, the value of a flag notdepicted in boldface, which means that flag is present in the bitstreamat the point where it occurs in the syntax diagram. Whether or notadaptive resolution is in use for this picture or parts thereof can besignaled in any high level syntax structure inside or outside thebitstream. In the example shown, it is signaled in the sequenceparameter set as outlined below.

Referring to FIG. 6B, shown is also an excerpt of a sequence parameterset (610). The first syntax element shown isadaptive_pic_resolution_change_flag (611). When true, that flag canindicate the use of adaptive resolution which, in turn may requirecertain control information. In the example, such control information isconditionally present based on the value of the flag based on the if( )statement in the parameter set (612) and the tile group header (601).

When adaptive resolution is in use, in this example, coded is an outputresolution in units of samples (613). The numeral 613 refers to bothoutput_pic_width_in_luma_samples and output_pic_height_in_luma_samples,which together can define the resolution of the output picture.Elsewhere in a video coding technology or standard, certain restrictionsto either value can be defined. For example, a level definition maylimit the number of total output samples, which could be the product ofthe value of those two syntax elements. Also, certain video codingtechnologies or standards, or external technologies or standards suchas, for example, system standards, may limit the numbering range (forexample, one or both dimensions must be divisible by a power of 2number), or the aspect ratio (for example, the width and height must bein a relation such as 4:3 or 16:9). Such restrictions may be introducedto facilitate hardware implementations or for other reasons, and arewell known in the art.

In certain applications, it can be advisable that the encoder instructsthe decoder to use a certain reference picture size rather thanimplicitly assume that size to be the output picture size. In thisexample, the syntax element reference_pic_size_present_flag (614) gatesthe conditional presence of reference picture dimensions (615) (again,the numeral refers to both width and height).

Finally, shown is a table of possible decoding picture width andheights. Such a table can be expressed, for example, by a tableindication (num_dec_pic_size_in_luma_samples_minus1) (616). The “minus1”can refer to the interpretation of the value of that syntax element. Forexample, if the coded value is zero, one table entry is present. If thevalue is five, six table entries are present. For each “line” in thetable, decoded picture width and height are then included in the syntax(617).

The table entries presented (617) can be indexed using the syntaxelement dec_pic_size_idx (602) in the tile group header, therebyallowing different decoded sizes—in effect, zoom factors—per tile group.

Certain video coding technologies or standards, for example VP9, supportspatial scalability by implementing certain forms of reference pictureresampling (signaled quite differently from the disclosed subjectmatter) in conjunction with temporal scalability, so to enable spatialscalability. In particular, certain reference pictures may be upsampledusing ARC-style technologies to a higher resolution to form the base ofa spatial enhancement layer. Those upsampled pictures could be refined,using normal prediction mechanisms at the high resolution, so to adddetail.

Embodiments discussed herein can be used in such an environment. Incertain cases, in the same or another embodiment, a value in the NALunit header, for example the Temporal ID field, can be used to indicatenot only the temporal but also the spatial layer. Doing so may havecertain advantages for certain system designs; for example, existingSelected Forwarding Units (SFU) created and optimized for temporal layerselected forwarding based on the NAL unit header Temporal ID value canbe used without modification, for scalable environments. In order toenable that, there may be a requirement for a mapping between the codedpicture size and the temporal layer is indicated by the temporal IDfield in the NAL unit header.

In some video coding technologies, an Access Unit (AU) can refer tocoded picture(s), slice(s), tile(s), NAL Unit(s), and so forth, thatwere captured and composed into a the respective picture/slice/tile/NALunit bitstream at a given instance in time. That instance in time canbe, for example, the composition time.

In HEVC, and certain other video coding technologies, a picture ordercount (POC) value can be used for indicating a selected referencepicture among multiple reference pictures stored in a decoded picturebuffer (DPB). When an access unit (AU) includes one or more pictures,slices, or tiles, each picture, slice, or tile belonging to the same AUmay carry the same POC value, from which it can be derived that theywere created from content of the same composition time. In other words,in a scenario where two pictures/slices/tiles carry the same given POCvalue, that can be indicative of the two picture/slice/tile belonging tothe same AU and having the same composition time. Conversely, twopictures/tiles/slices having different POC values can indicate thatthose pictures/slices/tiles belong to different AUs and have differentcomposition times.

In embodiments, this rigid relationship can be relaxed in that an accessunit can include pictures, slices, or tiles with different POC values.By allowing different POC values within an AU, it becomes possible touse the POC value to identify potentially independently decodablepictures/slices/tiles with identical presentation time. That, in turn,can enable support of multiple scalable layers without a change ofreference picture selection signaling, for example reference picture setsignaling or reference picture list signaling, as described in moredetail below.

It is, however, still desirable to be able to identify the AU apicture/slice/tile belongs to, with respect to otherpicture/slices/tiles having different POC values, from the POC valuealone. This can be achieved, as described below.

In embodiments, an access unit count (AUC) may be signaled in ahigh-level syntax structure, such as NAL unit header, slice header, tilegroup header, SEI message, parameter set or AU delimiter. The value ofAUC may be used to identify which NAL units, pictures, slices, or tilesbelong to a given AU. The value of AUC may be corresponding to adistinct composition time instance. The AUC value may be equal to amultiple of the POC value. By diving the POC value by an integer value,the AUC value may be calculated. In certain cases, division operationscan place a certain burden on decoder implementations. In such cases,small restrictions in the numbering space of the AUC values may allowsubstituting the division operation with shift operations. For example,the AUC value may be equal to a Most Significant Bit (MSB) value of thePOC value range.

In embodiments, a value of POC cycle per AU (poc_cycle_au) may besignaled in a high-level syntax structure, such as NAL unit header,slice header, tile group header, SEI message, parameter set or AUdelimiter. The poc_cycle_au may indicate how many different andconsecutive POC values can be associated with the same AU. For example,if the value of poc_cycle_au is equal to 4, the pictures, slices ortiles with the POC value equal to 0-3, inclusive, may be associated withthe AU with AUC value equal to 0, and the pictures, slices or tiles withPOC value equal to 4-7, inclusive, may be associated with the AU withAUC value equal to 1. Hence, the value of AUC may be inferred bydividing the POC value by the value of poc_cycle_au.

In embodiments, the value of poc_cyle_au may be derived frominformation, located for example in the video parameter set (VPS), thatidentifies the number of spatial or SNR layers in a coded videosequence. An example of such a possible relationship is brieflydescribed below. While the derivation as described above may save a fewbits in the VPS and hence may improve coding efficiency, in someembodiments the poc_cycle_au may be explicitly coded in an appropriatehigh level syntax structure hierarchically below the video parameterset, so to be able to minimize poc_cycle_au for a given small part of abitstream such as a picture. This optimization may save more bits thancan be saved through the derivation process above because POC values,and/or values of syntax elements indirectly referring to POC, may becoded in low level syntax structures.

In embodiments, FIG. 8 shows an example of syntax tables to signal thesyntax element of vps_poc_cycle_au in VPS (or SPS), which indicates thepoc_cycle_au used for all picture/slices in a coded video sequence, andthe syntax element of slice_poc_cycle_au, which indicates thepoc_cycle_au of the current slice, in slice header. If the POC valueincreases uniformly per AU, vps_contant_poc_cycle_per_au in VPS may beset equal to 1 and vps_poc_cycle_au may be signaled in VPS. In thiscase, slice_poc_cycle_au may be not explicitly signaled, and the valueof AUC for each AU may be calculated by dividing the value of POC byvps_poc_cycle_au. If the POC value does not increase uniformly per AU,vps_contant_poc_cycle_per_au in VPS may be set equal to 0. In this case,vps_access_unit_cnt may be not signaled, while slice_access_unit_cnt maybe signaled in slice header for each slice or picture. Each slice orpicture may have a different value of slice_access_unit_cnt. The valueof AUC for each AU may be calculated by dividing the value of POC byslice_poc_cycle_au.

FIG. 9 shows a block diagram illustrating an example of the processabove. For example, in operation S910, the VPS (or SPS) can be parsed,and it can be determined whether the POC cycle per AU is constant withinthe coded video sequence at operation S920. If the POC cycle per AU isconstant (YES at operation S920), then the value of access unit countfor a particular access unit can be calculated from the poc_cycle_ausignaled for the coded video sequence and a POC value of the particularaccess unit at operation S930. If the POC cycle per AU is not constant(NO at operation S920), then then the value of access unit count for aparticular access unit can be calculated from the poc_cycle_au signaledat the picture level and the POC value of the particular access unit atoperation S940. At operation S950, a new VPS (or SPS) can be parsed.

In embodiments, even though the value of POC of a picture, slice, ortile may be different, the picture, slice, or tile corresponding to anAU with the same AUC value may be associated with the same decoding oroutput time instance. Hence, without any inter-parsing/decodingdependency across pictures, slices or tiles in the same AU, all orsubset of pictures, slices or tiles associated with the same AU may bedecoded in parallel, and may be outputted at the same time instance.

In embodiments, even though the value of POC for a picture, slice, ortile may be different, the picture, slice, or tile corresponding to anAU with the same AUC value may be associated with the samecomposition/display time instance. When the composition time iscontained in a container format, even though pictures correspond todifferent AUs, if the pictures have the same composition time, thepictures can be displayed at the same time instance.

In embodiments, each picture, slice, or tile may have the same temporalidentifier (temporal_id) in the same AU. All or a subset of pictures,slices or tiles corresponding to a time instance may be associated withthe same temporal sub-layer. In embodiments, each picture, slice, ortile may have the same or a different spatial layer id (layer_id) in thesame AU. All or subset of pictures, slices or tiles corresponding to atime instance may be associated with the same or a different spatiallayer.

FIG. 7 shows an example of a video sequence structure with combinationof temporal_id, layer_id, POC and AUC values with adaptive resolutionchange. In this example, a picture, slice or tile in the first AU withAUC=0 may have temporal_id=0 and layer_id=0 or 1, while a picture, sliceor tile in the second AU with AUC=1 may have temporal_id=1 andlayer_id=0 or 1, respectively. The value of POC is increased by 1 perpicture regardless of the values of temporal_id and layer_id. In thisexample, the value of poc_cycle_au can be equal to 2. In embodiments,the value of poc_cycle_au may be set equal to the number of (spatialscalability) layers. In this example, hence, the value of POC isincreased by 2, while the value of AUC is increased by 1.

In the above embodiments, all or sub-set of inter-picture or inter-layerprediction structure and reference picture indication may be supportedby using the existing reference picture set (RPS) signaling in HEVC orthe reference picture list (RPL) signaling. In RPS or RPL, the selectedreference picture may be indicated by signaling the value of POC or thedelta value of POC between the current picture and the selectedreference picture. In embodiments, the RPS and RPL can be used toindicate the inter-picture or inter-layer prediction structure withoutchange of signaling, but with the following restrictions. If the valueof temporal_id of a reference picture is greater than the value oftemporal_id current picture, the current picture may not use thereference picture for motion compensation or other predictions. If thevalue of layer_id of a reference picture is greater than the value oflayer_id current picture, the current picture may not use the referencepicture for motion compensation or other predictions.

In embodiments, the motion vector scaling based on POC difference fortemporal motion vector prediction may be disabled across multiplepictures within an access unit. Hence, although each picture may have adifferent POC value within an access unit, the motion vector is notscaled and used for temporal motion vector prediction within an accessunit. This is because a reference picture with a different POC in thesame AU is considered a reference picture having the same time instance.Therefore, in the embodiment, the motion vector scaling function mayreturn 1, when the reference picture belongs to the AU associated withthe current picture.

In embodiments, the motion vector scaling based on POC difference fortemporal motion vector prediction may be optionally disabled acrossmultiple pictures, when the spatial resolution of the reference pictureis different from the spatial resolution of the current picture. Whenthe motion vector scaling is allowed, the motion vector is scaled basedon both POC difference and the spatial resolution ratio between thecurrent picture and the reference picture.

In embodiments, the motion vector may be scaled based on AUC differenceinstead of POC difference, for temporal motion vector prediction,especially when the poc_cycle_au has non-uniform value (for example whenvps_contant_poc_cycle_per_au==0). Otherwise (for example whenvps_contant_poc_cycle_per_au==1), the motion vector scaling based on AUCdifference may be identical to the motion vector scaling based on POCdifference.

In embodiments, when the motion vector is scaled based on AUCdifference, the reference motion vector in the same AU (with the sameAUC value) with the current picture is not scaled based on AUCdifference and used for motion vector prediction without scaling or withscaling based on spatial resolution ratio between the current pictureand the reference picture.

In embodiments, the AUC value may be used for identifying the boundaryof AU and used for hypothetical reference decoder (HRD) operation, whichneeds input and output timing with AU granularity. In embodiments, thedecoded picture with the highest layer in an AU may be outputted fordisplay. The AUC value and the layer_id value can be used foridentifying the output picture.

In embodiments, a picture may include of one or more sub-pictures. Eachsub-picture may cover a local region or the entire region of thepicture. The region supported by a sub-picture may or may not beoverlapped with the region supported by another sub-picture. The regioncovered by one or more sub-pictures may or may not cover the entireregion of a picture. If a picture includes a sub-picture, the regionsupported by the sub-picture may be identical to the region supported bythe picture.

In embodiments, a sub-picture may be coded by a coding method similar tothe coding method used for the coded picture. A sub-picture may beindependently coded or may be coded dependent on another sub-picture ora coded picture. A sub-picture may or may not have any parsingdependency from another sub-picture or a coded picture.

In embodiments, a coded sub-picture may be contained in one or morelayers. A coded sub-picture in a layer may have a different spatialresolution. The original sub-picture may be spatially re-sampled (forexample up-sampled or down-sampled), coded with different spatialresolution parameters, and contained in a bitstream corresponding to alayer.

In embodiments, a sub-picture with (W, H), where W indicates the widthof the sub-picture and H indicates the height of the sub-picture,respectively, may be coded and contained in the coded bitstreamcorresponding to layer 0, while the up-sampled (or down-sampled)sub-picture from the sub-picture with the original spatial resolution,with (W*S_(w,k), H*S_(h,k)), may be coded and contained in the codedbitstream corresponding to layer k, where S_(w,k), S_(h,k) indicate theresampling ratios, horizontally and vertically. If the values ofS_(w,k), S_(h,k) are greater than 1, the resampling may be up-sampling.Whereas, if the values of S_(w,k), S_(h,k) are smaller than 1, theresampling may be down-sampling.

In embodiments, a coded sub-picture in a layer may have a differentvisual quality from that of the coded sub-picture in another layer inthe same sub-picture or different subpicture. For example, sub-picture iin a layer, n, may be coded with the quantization parameter, Q_(i,n),while a sub-picture j in a layer, m, may be coded with the quantizationparameter, Q_(j,m).

In embodiments, a coded sub-picture in a layer may be independentlydecodable, without any parsing or decoding dependency from a codedsub-picture in another layer of the same local region. The sub-picturelayer, which can be independently decodable without referencing anothersub-picture layer of the same local region, may be the independentsub-picture layer. A coded sub-picture in the independent sub-picturelayer may or may not have a decoding or parsing dependency from apreviously coded sub-picture in the same sub-picture layer, but thecoded sub-picture may not have any dependency from a coded picture inanother sub-picture layer.

In embodiments, a coded sub-picture in a layer may be dependentlydecodable, with any parsing or decoding dependency from a codedsub-picture in another layer of the same local region. The sub-picturelayer, which can be dependently decodable with referencing anothersub-picture layer of the same local region, may be the dependentsub-picture layer. A coded sub-picture in the dependent sub-picture mayreference a coded sub-picture belonging to the same sub-picture, apreviously coded sub-picture in the same sub-picture layer, or bothreference sub-pictures.

In embodiments, a coded sub-picture may include one or more independentsub-picture layers and one or more dependent sub-picture layers.However, at least one independent sub-picture layer may be present for acoded sub-picture. A value of the layer identifier (layer_id), which maybe present in NAL unit header or another high-level syntax structure, ofthe independent sub-picture layer may be equal to 0. The sub-picturelayer with the layer_id equal to 0 may be the base sub-picture layer.

In embodiments, a picture may include one or more foregroundsub-pictures and one background sub-picture. The region supported by abackground sub-picture may be equal to the region of the picture. Theregion supported by a foreground sub-picture may be overlapped with theregion supported by a background sub-picture. The background sub-picturemay be a base sub-picture layer, while the foreground sub-picture may bea non-base (enhancement) sub-picture layer. One or more non-basesub-picture layers may reference the same base layer for decoding. Eachnon-base sub-picture layer with layer_id equal to a may reference anon-base sub-picture layer with layer_id equal to b, where a is greaterthan b.

In embodiments, a picture may include one or more foregroundsub-pictures with or without a background sub-picture. Each sub-picturemay have its own base sub-picture layer and one or more non-base(enhancement) layers. Each base sub-picture layer may be referenced byone or more non-base sub-picture layers. Each non-base sub-picture layerwith layer_id equal to a may reference a non-base sub-picture layer withlayer_id equal to b, where a is greater than b.

In embodiments, a picture may include one or more foregroundsub-pictures with or without a background sub-picture. Each codedsub-picture in a (base or non-base) sub-picture layer may be referencedby one or more non-base layer sub-pictures belonging to the samesub-picture and one or more non-base layer sub-pictures, which are notbelonging to the same sub-picture.

In embodiments, a picture may include one or more foregroundsub-pictures with or without a background sub-picture. A sub-picture ina layer a may be further partitioned into multiple sub-pictures in thesame layer. One or more coded sub-pictures in a layer b may referencethe partitioned sub-picture in a layer a.

In embodiments, a coded video sequence (CVS) may be a group of the codedpictures. The CVS may include one or more coded sub-picture sequences(CSPS), where the CSPS may be a group of coded sub-pictures covering thesame local region of the picture. A CSPS may have the same or adifferent temporal resolution than that of the coded video sequence.

In embodiments, a CSPS may be coded and contained in one or more layers.A CSPS may include one or more CSPS layers. Decoding one or more CSPSlayers corresponding to a CSPS may reconstruct a sequence ofsub-pictures corresponding to the same local region.

In embodiments, the number of CSPS layers corresponding to a CSPS may beidentical to or different from the number of CSPS layers correspondingto another CSPS.

In embodiments, a CSPS layer may have a different temporal resolution(e.g. frame rate) from another CSPS layer. The original (uncompressed)sub-picture sequence may be temporally re-sampled (for exampleup-sampled or down-sampled), coded with different temporal resolutionparameters, and contained in a bitstream corresponding to a layer.

In embodiments, a sub-picture sequence with the frame rate, F, may becoded and contained in the coded bitstream corresponding to layer 0,while the temporally up-sampled (or down-sampled) sub-picture sequencefrom the original sub-picture sequence, with F*S_(t,k), may be coded andcontained in the coded bitstream corresponding to layer k, where S_(t,k)indicates the temporal sampling ratio for layer k. If the value ofS_(t,k) is greater than 1, the temporal resampling process may be framerate up conversion. Whereas, if the value of S_(t,k) is smaller than 1,the temporal resampling process may be frame rate down conversion.

In embodiments, when a sub-picture with a CSPS layer a is referenced bya sub-picture with a CSPS layer b for motion compensation or anyinter-layer prediction, if the spatial resolution of the CSPS layer a isdifferent from the spatial resolution of the CSPS layer b, decodedpixels in the CSPS layer a are resampled and used for reference. Theresampling process may use an up-sampling filtering or a down-samplingfiltering.

FIG. 10 shows an example video stream including a background video CSPSwith layer_id equal to 0 and multiple foreground CSPS layers. While acoded sub-picture may include one or more CSPS layers, a backgroundregion, which does not belong to any foreground CSPS layer, may includea base layer. The base layer may contain a background region andforeground regions, while an enhancement CSPS layer may contain aforeground region. An enhancement CSPS layer may have a better visualquality than the base layer, at the same region. The enhancement CSPSlayer may reference the reconstructed pixels and the motion vectors ofthe base layer, corresponding to the same region.

In embodiments, the video bitstream corresponding to a base layer iscontained in a track, while the CSPS layers corresponding to eachsub-picture are contained in a separated track, in a video file.

In embodiments, the video bitstream corresponding to a base layer iscontained in a track, while CSPS layers with the same layer_id arecontained in a separated track. In this example, a track correspondingto a layer k includes CSPS layers corresponding to the layer k, only.

In embodiments, each CSPS layer of each sub-picture is stored in aseparate track. Each track may or may not have any parsing or decodingdependency from one or more other tracks.

In embodiments, each track may contain bitstreams corresponding to layeri to layer j of CSPS layers of all or a subset of sub-pictures, where0<i=<j=<k, k being the highest layer of CSPS.

In embodiments, a picture includes one or more associated media dataincluding depth map, alpha map, 3D geometry data, occupancy map, etc.Such associated timed media data can be divided to one or multiple datasub-stream each of which corresponding to one sub-picture.

FIG. 11 shows an example of video conference based on the multi-layeredsub-picture method. In a video stream, one base layer video bitstreamcorresponding to the background picture and one or more enhancementlayer video bitstreams corresponding to foreground sub-pictures arecontained. Each enhancement layer video bitstream may correspond to aCSPS layer. In a display, the picture corresponding to the base layer isdisplayed by default. It contains one or more user's picture in apicture (PIP). When a specific user is selected by a client's control,the enhancement CSPS layer corresponding to the selected user may bedecoded and displayed with the enhanced quality or spatial resolution.

FIG. 12 shows a block diagram illustrating an example of the processabove. For example, in operation S1210, a video bitstream with multiplelayers can be decoded. In operation S1220, a background region and oneor more foreground sub-pictures can be identified. At operation S1230,it can be determined whether a specific sub-picture region, for exampleone of the foreground sub-pictures, is selected. If a specificsub-picture region is selected (YES at operation S1240), an enhancedsub-picture may be decoded and displayed. If a specific sub-pictureregion is not selected (NO at operation S1240), the background regionmay be decoded and displayed

In embodiments, a network middle box (for example a router) may select asubset of layers to send to a user depending on its bandwidth. Thepicture/subpicture organization may be used for bandwidth adaptation.For instance, if the user doesn't have the bandwidth, the router stripsof layers or selects some subpictures due to their importance or basedon used setup and this can be done dynamically to adopt to bandwidth.

FIG. 13 shows an embodiment relating to a use case of 360 video. When aspherical 360 picture, for example picture 1310, is projected onto aplanar picture, the projection 360 picture may be partitioned intomultiple sub-pictures as a base layer. For example, the multiplesub-pictures may include a back sub-picture, a top sub-picture, a rightsub-picture, a left sub-picture, a forward sub-picture, and a bottomsub-picture. An enhancement layer of a specific sub-picture, for examplea forward sub-picture, may be coded and transmitted to a client. Adecoder may be able to decode both the base layer including allsub-pictures and an enhancement layer of a selected sub-picture. Whenthe current viewport is identical to the selected sub-picture, thedisplayed picture may have a higher quality with the decoded sub-picturewith the enhancement layer. Otherwise, the decoded picture with the baselayer can be displayed, with a lower quality.

In embodiments, any layout information for display may be present in afile, as supplementary information (such as SEI message or metadata).One or more decoded sub-pictures may be relocated and displayeddepending on the signaled layout information. The layout information maybe signaled by a streaming server or a broadcaster, or may beregenerated by a network entity or a cloud server, or may be determinedby a user's customized setting.

In embodiments, when an input picture is divided into one or more(rectangular) sub-region(s), each sub-region may be coded as anindependent layer. Each independent layer corresponding to a localregion may have a unique layer_id value. For each independent layer, thesub-picture size and location information may be signaled. For example,picture size (width, height), the offset information of the left-topcorner (x_offset, y_offset). FIG. 14 shows an example of the layout ofdivided sub-pictures, its sub-picture size and position information andits corresponding picture prediction structure. The layout informationincluding the sub-picture size(s) and the sub-picture position(s) may besignaled in a high-level syntax structure, such as parameter set(s),header of slice or tile group, or SEI message.

In embodiments, each sub-picture corresponding to an independent layermay have its unique POC value within an AU. When a reference pictureamong pictures stored in DPB is indicated by using syntax element(s) inRPS or RPL structure, the POC value(s) of each sub-picture correspondingto a layer may be used.

In embodiments, in order to indicate the (inter-layer) predictionstructure, the layer_id may not be used and the POC (delta) value may beused.

In embodiments, a sub-picture with a POC vale equal to N correspondingto a layer (or a local region) may or may not be used as a referencepicture of a sub-picture with a POC value equal to N+K, corresponding tothe same layer (or the same local region) for motion compensatedprediction. In most cases, the value of the number K may be equal to themaximum number of (independent) layers, which may be identical to thenumber of sub-regions.

In embodiments, FIG. 15 shows an extended case of FIG. 14 . When aninput picture is divided into multiple (e.g. four) sub-regions, eachlocal region may be coded with one or more layers. In the case, thenumber of independent layers may be equal to the number of sub-regions,and one or more layers may correspond to a sub-region. Thus, eachsub-region may be coded with one or more independent layer(s) and zeroor more dependent layer(s).

In embodiments, in FIG. 15 , the input picture may be divided into foursub-regions. As an example, the right-top sub-region may be coded as twolayers, which are layer 1 and layer 4, while the right-bottom sub-regionmay be coded as two layers, which are layer 3 and layer 5. In this case,the layer 4 may reference the layer 1 for motion compensated prediction,while the layer 5 may reference the layer 3 for motion compensation.

In embodiments, in-loop filtering (such as deblocking filtering,adaptive in-loop filtering, reshaper, bilateral filtering or anydeep-learning based filtering) across layer boundary may be (optionally)disabled.

In embodiments, motion compensated prediction or intra-block copy acrosslayer boundary may be (optionally) disabled.

In embodiments, boundary padding for motion compensated prediction orin-loop filtering at the boundary of sub-picture may be processedoptionally. A flag indicating whether the boundary padding is processedor not may be signaled in a high-level syntax structure, such asparameter set(s) (VPS, SPS, PPS, or APS), slice or tile group header, orSEI message.

In embodiments, the layout information of sub-region(s) (orsub-picture(s)) may be signaled in VPS or SPS. FIG. 16A shows an exampleof the syntax elements in VPS, and FIG. 16B shows an example of thesyntax elements in SPS. In this example, vps_sub_picture_dividing_flagis signaled in VPS. The flag may indicate whether input picture(s) aredivided into multiple sub-regions or not. When the value ofvps_sub_picture_dividing_flag is equal to 0, the input picture(s) in thecoded video sequence(s) corresponding to the current VPS may not bedivided into multiple sub-regions. In this case, the input picture sizemay be equal to the coded picture size (pic_width_in_luma_samples,pic_height_in_luma_samples), which is signaled in SPS. When the value ofvps_sub_picture_dividing_flag is equal to 1, the input picture(s) may bedivided into multiple sub-regions. In this case, the syntax elementsvps_full_pic_width_in_luma_samples andvps_full_pic_height_in_luma_samples are signaled in VPS. The values ofvps_full_pic_width_in_luma_samples andvps_full_pic_height_in_luma_samples may be equal to the width and heightof the input picture(s), respectively.

In embodiments, the values of vps_full_pic_width_in_luma_samples andvps_full_pic_height_in_luma_samples may not be used for decoding, butmay be used for composition and display.

In embodiments, when the value of vps_sub_picture_dividing_flag is equalto 1, the syntax elements pic_offset_x and pic_offset_y may be signaledin SPS, which corresponds to (a) specific layer(s). In this case, thecoded picture size (pic_width_in_luma_samples,pic_height_in_luma_samples) signaled in SPS may be equal to the widthand height of the sub-region corresponding to a specific layer. Also,the position (pic_offset_x, pic_offset_y) of the left-top corner of thesub-region may be signaled in SPS.

In embodiments, the position information (pic_offset_x, pic_offset_y) ofthe left-top corner of the sub-region may not be used for decoding, butmay be used for composition and display.

In embodiments, the layout information (size and position) of all orsub-set sub-region(s) of (an) input picture(s), the dependencyinformation between layer(s) may be signaled in a parameter set or anSEI message. FIG. 17 shows an example of syntax elements to indicate theinformation of the layout of sub-regions, the dependency between layers,and the relation between a sub-region and one or more layers. In thisexample, the syntax element num_sub_region indicates the number of(rectangular) sub-regions in the current coded video sequence. thesyntax element num_layers indicates the number of layers in the currentcoded video sequence. The value of num_layers may be equal to or greaterthan the value of num_sub_region. When any sub-region is coded as asingle layer, the value of num_layers may be equal to the value ofnum_sub_region. When one or more sub-regions are coded as multiplelayers, the value of num_layers may be greater than the value ofnum_sub_region. The syntax element direct_dependency_flag[i][j]indicates the dependency from the j-th layer to the i-th layer.num_layers_for_region[i] indicates the number of layers associated withthe i-th sub-region. sub_region_layer_id[i][j] indicates the layer_id ofthe j-th layer associated with the i-th sub-region. Thesub_region_offset_x[i] and sub_region_offset_y[i] indicate thehorizontal and vertical location of the left-top corner of the i-thsub-region, respectively. The sub_region_width [i] andsub_region_height[i] indicate the width and height of the i-thsub-region, respectively.

In embodiments, one or more syntax elements that specify the outputlayer set to indicate one of more layers to be outputted with or withoutprofile tier level information may be signaled in a high-level syntaxstructure, e.g. VPS, DPS, SPS, PPS, APS or SEI message. Referring toFIG. 18 , the syntax element num_output_layer_sets indicating the numberof output layer set (OLS) in the coded vide sequence referring to theVPS may be signaled in the VPS. For each output layer set,output_layer_flag may be signaled as many as the number of outputlayers.

In embodiments, output_layer_flag[i] equal to 1 specifies that the i-thlayer is output. vps_output_layer_flag[i] equal to 0 specifies that thei-th layer is not output.

In embodiments, one or more syntax elements that specify the profiletier level information for each output layer set may be signaled in ahigh-level syntax structure, e.g. VPS, DPS, SPS, PPS, APS or SEImessage. Still referring to FIG. 18 , the syntax elementnum_profile_tile_level indicating the number of profile tier levelinformation per OLS in the coded vide sequence referring to the VPS maybe signaled in the VPS. For each output layer set, a set of syntaxelements for profile tier level information or an index indicating aspecific profile tier level information among entries in the profiletier level information may be signaled as many as the number of outputlayers.

In embodiments, profile_tier_level_idx[i][j] specifies the index, intothe list of profile_tier_level( ) syntax structures in the VPS, of theprofile_tier_level( ) syntax structure that applies to the j-th layer ofthe i-th OLS.

In embodiments, referring to FIG. 19 , the syntax elementsnum_profile_tile_level and/or num_output_layer_sets may be signaled whenthe number of maximum layers is greater than 1(vps_max_layers_minus1>0).

In embodiments, referring to FIG. 19 , the syntax elementvps_output_layers_mode[i] indicating the mode of output layer signalingfor the i-th output layer set may be present in VPS.

In embodiments, vps_output_layers_mode[i] equal to 0 specifies that onlythe highest layer is output with the i-th output layer set.vps_output_layer_mode[i] equal to 1 specifies that all layers are outputwith the i-th output layer set. vps_output layer mode[i] equal to 2specifies that the layers that are output are the layers withvps_output_layer_flag[i][j] equal to 1 with the i-th output layer set.More values may be reserved.

In embodiments, the output_layer_flag[i][j] may or may not be signaleddepending on the value of vps_output_layers_mode[i] for the i-th outputlayer set.

In embodiments, referring to FIG. 19 , the flag vps_ptl_signal_flag[i]may be present for the i-th output layer set. Depending the value ofvps_ptl_signal_flag[i], the profile tier level information for the i-thoutput layer set may or may not be signaled.

In embodiments, referring to FIG. 20 , the number of subpicture,max_subpics_minus1, in the current CVS may be signaled in a high-levelsyntax structure, e.g. VPS, DPS, SPS, PPS, APS or SEI message.

In embodiments, referring to FIG. 20 , the subpicture identifier,sub_pic_id[i], for the i-th subpicture may be signaled, when the numberof subpictures is greater than 1 (max_subpics_minus1>0).

In embodiments, one or more syntax elements indicating the subpictureidentifier belonging to each layer of each output layer set may besignaled in VPS. Referring to FIG. 20 , the sub_pic_id_layer[i][j][k],which indicates the k-th subpicture present in the j-th layer of thei-th output layer set. With this information, a decoder may recognizewhich sub-picture may be decoded and outputtted for each layer of aspecific output layer set.

In embodiments, picture header (PH) is a syntax structure containingsyntax elements that apply to all slices of a coded picture. A pictureunit (PU) is a set of NAL units that are associated with each otheraccording to a specified classification rule, are consecutive indecoding order, and contain exactly one coded picture. A PU may containa picture header (PH) and one or more coded slice NAL units or VCL NALunits composing a coded picture.

In embodiments, an SPS (RBSP) may be available to the decoding processprior to it being referenced, included in at least one AU withTemporalId equal to 0 or provided through external means.

In embodiments, an SPS (RBSP) may be available to the decoding processprior to it being referenced, included in at least one AU withTemporalId equal to 0 in the CVS, which contains one or more PPSreferring to the SPS, or provided through external means.

In embodiments, an SPS (RBSP) may be available to the decoding processprior to it being referenced by one or more PPS, included in at leastone PU with nuh_layer_id equal to the lowest nuh_layer_id value of thePPS NAL units that refer to the SPS NAL unit in the CVS, which containsone or more PPS referring to the SPS, or provided through externalmeans.

In embodiments, an SPS (RBSP) may be available to the decoding processprior to it being referenced by one or more PPS, included in at leastone PU with TemporalId equal to 0 and nuh_layer_id equal to the lowestnuh_layer_id value of the PPS NAL units that refer to the SPS NAL unitor provided through external means.

In embodiments, an SPS (RBSP) may be available to the decoding processprior to it being referenced by one or more PPS, included in at leastone PU with TemporalId equal to 0 and nuh_layer_id equal to the lowestnuh_layer_id value of the PPS NAL units that refer to the SPS NAL unitin the CVS, which contains one or more PPS referring to the SPS, orprovided through external means or provided through external means.

In embodiments, pps_seq_parameter_set_id specifies the value ofsps_seq_parameter_set_id for the referenced SPS. The value ofpps_seq_parameter_set_id may be the same in all PPSs that are referredto by coded pictures in a CLVS.

In embodiments, all SPS NAL units with a particular value ofsps_seq_parameter_set_id in a CVS may have the same content.

In embodiments, regardless of the nuh_layer_id values, SPS NAL units mayshare the same value space of sps_seq_parameter_set_id.

In embodiments, the nuh_layer_id value of a SPS NAL unit may be equal tothe lowest nuh_layer_id value of the PPS NAL units that refer to the SPSNAL unit.

In embodiments, when an SPS with nuh_layer_id equal to m is referred toby one or more PPS with nuh_layer_id equal to n. the layer withnuh_layer_id equal to m may be the same as the layer with nuh_layer_idequal to n or a (direct or indirect) reference layer of the layer withnuh_layer_id equal to m.

In embodiments, a PPS (RBSP) shall be available to the decoding processprior to it being referenced, included in at least one AU withTemporalId equal to the TemporalId of the PPS NAL unit or providedthrough external means.

In embodiments, a PPS (RBSP) may be available to the decoding processprior to it being referenced, included in at least one AU withTemporalId equal to the TemporalId of the PPS NAL unit in the CVS, whichcontains one or more PHs (or coded slice NAL units) referring to thePPS, or provided through external means.

In embodiments, a PPS (RBSP) may be available to the decoding processprior to it being referenced by one or more PHs (or coded slice NALunits), included in at least one PU with nuh_layer_id equal to thelowest nuh_layer_id value of the coded slice NAL units that refer to thePPS NAL unit in the CVS, which contains one or more PHs (or coded sliceNAL units) referring to the PPS, or provided through external means.

In embodiments, a PPS (RBSP) may be available to the decoding processprior to it being referenced by one or more PHs (or coded slice NALunits), included in at least one PU with TemporalId equal to theTemporalId of the PPS NAL unit and nuh_layer_id equal to the lowestnuh_layer_id value of the coded slice NAL units that refer to the PPSNAL unit in the CVS, which contains one or more PHs (or coded slice NALunits) referring to the PPS, or provided through external means.

In embodiments, ph_pic_parameter_set_id in PH specifies the value ofpps_pic_parameter_set_id for the referenced PPS in use. The value ofpps_seq_parameter set id may be the same in all PPSs that are referredto by coded pictures in a CLVS.

In embodiments, All PPS NAL units with a particular value ofpps_pic_parameter_set_id within a PU shall have the same content.

In embodiments, regardless of the nuh_layer_id values, PPS NAL units mayshare the same value space of pps_pic_parameter_set_id.

In embodiments, the nuh_layer_id value of a PPS NAL unit may be equal tothe lowest nuh_layer_id value of the coded slice NAL units that refer tothe NAL unit that refer to the PPS NAL unit.

In embodiments, when a PPS with nuh_layer_id equal to m is referred toby one or more coded slice NAL units with nuh_layer_id equal to n. thelayer with nuh_layer_id equal to m may be the same as the layer withnuh_layer_id equal to n or a (direct or indirect) reference layer of thelayer with nuh_layer_id equal to m.

In embodiments, a PPS (RBSP) shall be available to the decoding processprior to it being referenced, included in at least one AU withTemporalId equal to the TemporalId of the PPS NAL unit or providedthrough external means.

In embodiments, a PPS (RBSP) may be available to the decoding processprior to it being referenced, included in at least one AU withTemporalId equal to the TemporalId of the PPS NAL unit in the CVS, whichcontains one or more PHs (or coded slice NAL units) referring to thePPS, or provided through external means.

In embodiments, a PPS (RBSP) may be available to the decoding processprior to it being referenced by one or more PHs (or coded slice NALunits), included in at least one PU with nuh_layer_id equal to thelowest nuh_layer_id value of the coded slice NAL units that refer to thePPS NAL unit in the CVS, which contains one or more PHs (or coded sliceNAL units) referring to the PPS, or provided through external means.

In embodiments, a PPS (RBSP) may be available to the decoding processprior to it being referenced by one or more PHs (or coded slice NALunits), included in at least one PU with TemporalId equal to theTemporalId of the PPS NAL unit and nuh_layer_id equal to the lowestnuh_layer_id value of the coded slice NAL units that refer to the PPSNAL unit in the CVS, which contains one or more PHs (or coded slice NALunits) referring to the PPS, or provided through external means.

In embodiments, ph_pic_parameter_set_id in PH specifies the value ofpps_pic_parameter_set_id for the referenced PPS in use. The value ofpps_seq_parameter_set_id may be the same in all PPSs that are referredto by coded pictures in a CLVS.

In embodiments, All PPS NAL units with a particular value ofpps_pic_parameter_set_id within a PU shall have the same content.

In embodiments, regardless of the nuh_layer_id values, PPS NAL units mayshare the same value space of pps_pic_parameter_set_id.

In embodiments, the nuh_layer_id value of a PPS NAL unit may be equal tothe lowest nuh_layer_id value of the coded slice NAL units that refer tothe NAL unit that refer to the PPS NAL unit.

In embodiments, when a PPS with nuh_layer_id equal to m is referred toby one or more coded slice NAL units with nuh_layer_id equal to n. thelayer with nuh_layer_id equal to m may be the same as the layer withnuh_layer_id equal to n or a (direct or indirect) reference layer of thelayer with nuh_layer_id equal to m.

In embodiments, when a flag, no temporal sublayer switching flag issignaled in a DPS, VPS, or SPS, the TemporalId value of a PPS referringto the parameter set containing the flag equal to 1 may be equal to 0,while the TemporalId value of a PPS referring to the parameter setcontaining the flag equal to 1 may be equal to or greater than theTemporalId value of the parameter set.

In embodiments, each PPS (RBSP) may be available to the decoding processprior to it being referenced, included in at least one AU withTemporalId less than or equal to the TemporalId of the coded slice NALunit (or PH NAL unit) that refers it or provided through external means.When the PPS NAL unit is included in an AU prior to the AU containingthe coded slice NAL unit referring to the PPS, a VCL NAL unit enabling atemporal up-layer switching or a VCL NAL unit with nal_unit_type equalto STSA_NUT, which indicates that the picture in the VCL NAL unit may bea step-wise temporal sublayer access (STSA) picture, may not be presentsubsequent to the PPS NAL unit and prior to the coded slice NAL unitreferring to the PPS.

In embodiments, the PPS NAL unit and the coded slice NAL unit (and itsPH NAL unit) referring to the PPS may be included in the same AU.

In embodiments, the PPS NAL unit and the STSA NAL unit may be includedin the same AU, which is prior to the coded slice NAL unit (and its PHNAL unit) referring to the PPS.

In embodiments, the STSA NAL unit, the PPS NAL unit and the coded sliceNAL unit (and its PH NAL unit) referring to the PPS may be present inthe same AU.

In the same embodiment, the TemporalId value of the VCL NAL unitcontaining an PPS may be equal to the TemporalId value of the prior STSANAL unit.

In the same embodiment, the picture order count (POC) value of the PPSNAL unit may be equal to or greater than the POC value of the STSA NALunit.

In the same embodiment, the picture order count (POC) value of the codedslice or PH NAL unit, which refers to the PPS NAL unit, may be equal toor greater than the POC value of the referenced PPS NAL unit.

FIG. 21 is a flowchart is an example process 2100 for decoding anencoded video bitstream. In some implementations, one or more processblocks of FIG. 21 may be performed by decoder 210. In someimplementations, one or more process blocks of FIG. 21 may be performedby another device or a group of devices separate from or includingdecoder 210, such as encoder 203.

As shown in FIG. 21 , process 2100 may include obtaining a coded videosequence from the encoded video bitstream (block 2110).

As further shown in FIG. 21 , process 2100 may include obtaining apicture unit from the coded video sequence (block 2120).

As further shown in FIG. 21 , process 2100 may include obtaining a PHNAL unit included in the picture unit (block 2130).

As further shown in FIG. 21 , process 2100 may include obtaining atleast one coded slice NAL unit included in the picture unit (block2140).

As further shown in FIG. 21 , process 2100 may include decoding a codedpicture based on the PH NAL unit, the at least one coded slice NAL unit,a PPS included in a PPS NAL unit obtained from the coded video sequence,and an SPS included in an SPS NAL unit obtained from the coded videosequence, wherein the SPS NAL unit is available to at least oneprocessor executing the process 2100 before the PPS NAL unit, andwherein the PPS NAL unit is available to the at least one processorbefore the PH NAL unit and the at least one coded slice NAL unit (block2150).

As further shown in FIG. 21 , process 2100 may include outputting thedecoded picture (block 2160).

In embodiments, a temporal identifier of the SPS NAL unit may be equalto zero.

In embodiments, a layer identifier of the PPS NAL unit is greater thanor equal to a layer identifier of the SPS NAL unit.

In embodiments, a layer identifier of the at least one coded slice NALunit may be greater than or equal to a layer identifier of the PPS NALunit.

In embodiments, the PH NAL unit, the at least one coded slice NAL unit,and the PPS NAL unit may be included in a single access unit.

In embodiments, the coded video sequence may further include a step-wisetemporal sublayer access (STSA) NAL unit corresponding to an STSApicture, and the STSA NAL unit is not located between the PPS NAL unitand the at least one coded slice NAL unit.

In embodiments, the at least one coded slice NAL unit, the PPS NAL unit,and the STSA NAL unit may be included in a single access unit.

In embodiments, a temporal identifier of the PPS NAL unit may be equalto a temporal identifier of the STSA NAL unit.

In embodiments, a picture order count (POC) of the PPS NAL unit may beis greater than or equal to a POC of the STSA NAL unit.

Although FIG. 21 shows example blocks of process 2100, in someimplementations, process 2100 may include additional blocks, fewerblocks, different blocks, or differently arranged blocks than thosedepicted in FIG. 21 Additionally, or alternatively, two or more of theblocks of process 2100 may be performed in parallel.

Further, the proposed methods may be implemented by processing circuitry(e.g., one or more processors or one or more integrated circuits). Inone example, the one or more processors execute a program that is storedin a non-transitory computer-readable medium to perform one or more ofthe proposed methods.

The techniques described above can be implemented as computer softwareusing computer-readable instructions and physically stored in one ormore computer-readable media. For example, FIG. 22 shows a computersystem 2200 suitable for implementing certain embodiments of thedisclosed subject matter.

The computer software can be coded using any suitable machine code orcomputer language, that may be subject to assembly, compilation,linking, or like mechanisms to create code comprising instructions thatcan be executed directly, or through interpretation, micro-codeexecution, and the like, by computer central processing units (CPUs),Graphics Processing Units (GPUs), and the like.

The instructions can be executed on various types of computers orcomponents thereof, including, for example, personal computers, tabletcomputers, servers, smartphones, gaming devices, internet of thingsdevices, and the like.

The components shown in FIG. 22 for computer system 2200 are exemplaryin nature and are not intended to suggest any limitation as to the scopeof use or functionality of the computer software implementingembodiments of the present disclosure. Neither should the configurationof components be interpreted as having any dependency or requirementrelating to any one or combination of components illustrated in theexemplary embodiment of a computer system 2300.

Computer system 2200 may include certain human interface input devices.Such a human interface input device may be responsive to input by one ormore human users through, for example, tactile input (such as:keystrokes, swipes, data glove movements), audio input (such as: voice,clapping), visual input (such as: gestures), olfactory input (notdepicted). The human interface devices can also be used to capturecertain media not necessarily directly related to conscious input by ahuman, such as audio (such as: speech, music, ambient sound), images(such as: scanned images, photographic images obtain from a still imagecamera), video (such as two-dimensional video, three-dimensional videoincluding stereoscopic video).

Input human interface devices may include one or more of (only one ofeach depicted): keyboard 2201, mouse 2202, trackpad 2203, touch screen2210 and associated graphics adapter 2250, data-glove, joystick 2205,microphone 2206, scanner 2207, camera 2208.

Computer system 2200 may also include certain human interface outputdevices. Such human interface output devices may be stimulating thesenses of one or more human users through, for example, tactile output,sound, light, and smell/taste. Such human interface output devices mayinclude tactile output devices (for example tactile feedback by thetouch-screen 2210, data-glove, or joystick 2205, but there can also betactile feedback devices that do not serve as input devices), audiooutput devices (such as: speakers 2209, headphones (not depicted)),visual output devices (such as screens 2210 to include cathode ray tube(CRT) screens, liquid-crystal display (LCD) screens, plasma screens,organic light-emitting diode (OLED) screens, each with or withouttouch-screen input capability, each with or without tactile feedbackcapability—some of which may be capable to output two dimensional visualoutput or more than three dimensional output through means such asstereographic output; virtual-reality glasses (not depicted),holographic displays and smoke tanks (not depicted)), and printers (notdepicted).

Computer system 2200 can also include human accessible storage devicesand their associated media such as optical media including CD/DVD ROM/RW2220 with CD/DVD or the like media 2221, thumb-drive 2222, removablehard drive or solid state drive 2223, legacy magnetic media such as tapeand floppy disc (not depicted), specialized ROM/ASIC/PLD based devicessuch as security dongles (not depicted), and the like.

Those skilled in the art should also understand that term “computerreadable media” as used in connection with the presently disclosedsubject matter does not encompass transmission media, carrier waves, orother transitory signals.

Computer system 2200 can also include interface(s) to one or morecommunication networks (955). Networks can for example be wireless,wireline, optical. Networks can further be local, wide-area,metropolitan, vehicular and industrial, real-time, delay-tolerant, andso on. Examples of networks include local area networks such asEthernet, wireless LANs, cellular networks to include global systems formobile communications (GSM), third generation (3G), fourth generation(4G), fifth generation (5G), Long-Term Evolution (LTE), and the like, TVwireline or wireless wide area digital networks to include cable TV,satellite TV, and terrestrial broadcast TV, vehicular and industrial toinclude CANBus, and so forth. Certain networks commonly require externalnetwork interface adapters (954) that attached to certain generalpurpose data ports or peripheral buses (949) (such as, for exampleuniversal serial bus (USB) ports of the computer system 2200; others arecommonly integrated into the core of the computer system 2200 byattachment to a system bus as described below (for example Ethernetinterface into a PC computer system or cellular network interface into asmartphone computer system). As an example, network 2255 may beconnected to peripheral bus 2249 using network interface 2254. Using anyof these networks, computer system 2200 can communicate with otherentities. Such communication can be uni-directional, receive only (forexample, broadcast TV), uni-directional send-only (for example CANbus tocertain CANbus devices), or bi-directional, for example to othercomputer systems using local or wide area digital networks. Certainprotocols and protocol stacks can be used on each of those networks andnetwork interfaces (954) as described above.

Aforementioned human interface devices, human-accessible storagedevices, and network interfaces can be attached to a core 2240 of thecomputer system 2200.

The core 2240 can include one or more Central Processing Units (CPU)2241, Graphics Processing Units (GPU) 2242, specialized programmableprocessing units in the form of Field Programmable Gate Areas (FPGA)2243, hardware accelerators 2244 for certain tasks, and so forth. Thesedevices, along with Read-only memory (ROM) 2245, Random-access memory(RAM) 2246, internal mass storage such as internal non-user accessiblehard drives, solid-state drives (SSDs), and the like 2247, may beconnected through a system bus 2248. In some computer systems, thesystem bus 2248 can be accessible in the form of one or more physicalplugs to enable extensions by additional CPUs, GPU, and the like. Theperipheral devices can be attached either directly to the core's systembus 2248, or through a peripheral bus 2249. Architectures for aperipheral bus include peripheral component interconnect (PCI), USB, andthe like.

CPUs 2241, GPUs 2242, FPGAs 2243, and accelerators 2244 can executecertain instructions that, in combination, can make up theaforementioned computer code. That computer code can be stored in ROM2245 or RAM 2246. Transitional data can be also be stored in RAM 2246,whereas permanent data can be stored for example, in the internal massstorage 2247. Fast storage and retrieve to any of the memory devices canbe enabled through the use of cache memory, that can be closelyassociated with one or more CPU 2241, GPU 2242, mass storage 2247, ROM2245, RAM 2246, and the like.

The computer readable media can have computer code thereon forperforming various computer-implemented operations. The media andcomputer code can be those specially designed and constructed for thepurposes of the present disclosure, or they can be of the kind wellknown and available to those having skill in the computer software arts.

As an example and not by way of limitation, the computer system havingarchitecture 2200, and specifically the core 2240 can providefunctionality as a result of processor(s) (including CPUs, GPUs, FPGA,accelerators, and the like) executing software embodied in one or moretangible, computer-readable media. Such computer-readable media can bemedia associated with user-accessible mass storage as introduced above,as well as certain storage of the core 2240 that are of non-transitorynature, such as core-internal mass storage 2247 or ROM 2245. Thesoftware implementing various embodiments of the present disclosure canbe stored in such devices and executed by core 2240. A computer-readablemedium can include one or more memory devices or chips, according toparticular needs. The software can cause the core 2240 and specificallythe processors therein (including CPU, GPU, FPGA, and the like) toexecute particular processes or particular parts of particular processesdescribed herein, including defining data structures stored in RAM 2246and modifying such data structures according to the processes defined bythe software. In addition or as an alternative, the computer system canprovide functionality as a result of logic hardwired or otherwiseembodied in a circuit (for example: accelerator 2244), which can operatein place of or together with software to execute particular processes orparticular parts of particular processes described herein. Reference tosoftware can encompass logic, and vice versa, where appropriate.Reference to a computer-readable media can encompass a circuit (such asan integrated circuit (IC)) storing software for execution, a circuitembodying logic for execution, or both, where appropriate. The presentdisclosure encompasses any suitable combination of hardware andsoftware.

While this disclosure has described several exemplary embodiments, thereare alterations, permutations, and various substitute equivalents, whichfall within the scope of the disclosure. It will thus be appreciatedthat those skilled in the art will be able to devise numerous systemsand methods which, although not explicitly shown or described herein,embody the principles of the disclosure and are thus within the spiritand scope thereof.

What is claimed is:
 1. A method of decoding an encoded video bitstreamusing at least one processor, the method comprising: obtaining a codedvideo sequence from the encoded video bitstream; obtaining a pictureunit from the coded video sequence; obtaining a picture header (PH)network abstraction layer (NAL) unit included in the picture unit;obtaining at least one coded slice NAL unit corresponding to the PH NALunit; obtaining a picture parameter set (PPS) included in a PPS NAL unitfrom the coded video sequence, wherein the PPS NAL unit is referenced bythe PH NAL unit and the coded slice NAL unit, and wherein the PPS NALunit includes a first layer identifier of the PPS NAL unit; obtaining asequence parameter set (SPS) included in an SPS NAL unit obtained fromthe coded video sequence, wherein the SPS NAL unit, which includes theSPS, is directly referenced by the PPS NAL unit, wherein the SPS NALunit includes a second layer identifier of the SPS NAL unit, and whereina value of the first layer identifier of the PPS NAL unit is greaterthan a value of the second layer identifier of the SPS NAL unit;decoding a coded picture based on the PH NAL unit, the at least onecoded slice NAL unit, the PPS NAL unit, and the SPS NAL unit; andoutputting the decoded picture, wherein the SPS NAL unit is available tothe at least one processor before the PPS NAL unit, and wherein the PPSNAL unit is available to the at least one processor before the PH NALunit and the at least one coded slice NAL unit.
 2. The method of claim1, wherein a temporal identifier of the SPS NAL unit is equal to zero.3. The method of claim 1, wherein a layer identifier of the at least onecoded slice NAL unit is greater than or equal to the layer identifier ofthe PPS NAL unit.
 4. The method of claim 1, wherein the PH NAL unit, theat least one coded slice NAL unit, and the PPS NAL unit are included ina single access unit.
 5. The method of claim 1, wherein the coded videosequence further comprises a step-wise temporal sublayer access (STSA)NAL unit corresponding to an STSA picture, and wherein the STSA NAL unitis not located between the PPS NAL unit and the at least one coded sliceNAL unit.
 6. The method of claim 5, wherein the PH NAL unit, the atleast one coded slice NAL unit, the PPS NAL unit, and the STSA NAL unitare included in a single access unit.
 7. The method of claim 5, whereina temporal identifier of the PPS NAL unit is equal to a temporalidentifier of the STSA NAL unit.
 8. The method of claim 5, wherein apicture order count (POC) of the PPS NAL unit is greater than or equalto a POC of the STSA NAL unit.
 9. A device for decoding an encoded videobitstream, the device comprising: at least one memory configured tostore program code; and at least one processor configured to read theprogram code and operate as instructed by the program code, the programcode including: first obtaining code configured to cause the at leastone processor to obtain a coded video sequence from the encoded videobitstream; second obtaining code configured to cause the at least oneprocessor to obtain a picture unit from the coded video sequence; thirdobtaining code configured to cause the at least one processor to obtaina picture header (PH) network abstraction layer (NAL) unit included inthe picture unit; fourth obtaining code configured to cause the at leastone processor to obtain at least one coded slice NAL unit correspondingto the PH NAL unit; fifth obtaining code configured to cause the atleast one processor to obtain a picture parameter set (PPS) included ina PPS NAL unit from the coded video sequence, wherein the PPS NAL unitis referenced by the PH NAL unit and the coded slice NAL unit, andwherein the PPS NAL unit includes a first layer identifier of the PPSNAL unit; sixth obtaining code configured to cause the at least oneprocessor to obtain a sequence parameter set (SPS) included in an SPSNAL unit obtained from the coded video sequence, wherein the SPS NALunit, which includes the SPS, is directly referenced by the PPS NALunit, wherein the SPS NAL unit includes a second layer identifier of theSPS NAL unit, and wherein a value of the first layer identifier of thePPS NAL unit is greater than a value of the second layer identifier ofthe SPS NAL unit; decoding code configured to cause the at least oneprocessor to a coded picture based on the PH NAL unit, the at least onecoded slice NAL unit, the PPS, and the SPS; and output code configuredto cause the at least one processor to output the decoded picture,wherein the SPS NAL unit is available to the at least one processorbefore the PPS NAL unit, and wherein the PPS NAL unit is available tothe at least one processor before the PH NAL unit and the at least onecoded slice NAL unit.
 10. The device of claim 9, wherein a temporalidentifier of the SPS NAL unit is equal to zero.
 11. The device of claim9, wherein a layer identifier of the at least one coded slice NAL unitis greater than or equal to the layer identifier of the PPS NAL unit.12. The device of claim 9, wherein the PH NAL unit, the at least onecoded slice NAL unit, and the PPS NAL unit are included in a singleaccess unit.
 13. The device of claim 9, wherein the coded video sequencefurther comprises a step-wise temporal sublayer access (STSA) NAL unitcorresponding to an STSA picture, and wherein the STSA NAL unit is notlocated between the PPS NAL unit and the at least one coded slice NALunit.
 14. The device of claim 13, wherein the PH NAL unit, the at leastone coded slice NAL unit, the PPS NAL unit, and the STSA NAL unit areincluded in a single access unit.
 15. The device of claim 13, wherein atemporal identifier of the PPS NAL unit is equal to a temporalidentifier of the STSA NAL unit.
 16. The device of claim 13, wherein apicture order count (POC) of the PPS NAL unit is greater than or equalto a POC of the STSA NAL unit.
 17. A non-transitory computer-readablemedium storing instructions, the instructions comprising: one or moreinstructions that, when executed by one or more processors of a devicefor decoding an encoded video bitstream, cause the one or moreprocessors to: obtain a coded video sequence from the encoded videobitstream; obtain a picture unit from the coded video sequence; obtain apicture header (PH) network abstraction layer (NAL) unit included in thepicture unit; obtain at least one coded slice NAL unit corresponding tothe PH NAL unit; obtain a picture parameter set (PPS) included in a PPSNAL unit from the coded video sequence, wherein the PPS NAL unit isreferenced by the PH NAL unit and the coded slice NAL unit, and whereinthe PPS NAL unit includes a first layer identifier of the PPS NAL unit;obtain a sequence parameter set (SPS) included in an SPS NAL unitobtained from the coded video sequence, wherein the SPS NAL unit, whichincludes the SPS, is directly referenced by the PPS NAL unit, whereinthe SPS NAL unit includes a second layer identifier of the SPS NAL unit,and wherein a value of the first layer identifier of the PPS NAL unit isgreater than a value of the second layer identifier of the SPS NAL unit;decode a coded picture based on the PH NAL unit, the at least one codedslice NAL unit, a picture parameter set (PPS) included in a PPS NAL unitobtained from the coded video sequence, and a sequence parameter set(SPS) included in an SPS NAL unit obtained from the coded videosequence; and output the decoded picture, wherein the SPS NAL unit isavailable to one or more processors before the PPS NAL unit, and whereinthe PPS NAL unit is available one or more processors before the PH NALunit and the at least one coded slice NAL unit.
 18. The non-transitorycomputer-readable medium of claim 17, wherein a temporal identifier ofthe SPS NAL unit is equal to zero.